Is My Oil Temperature Too High??

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Steven R

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Steve R
Hello all. I have a 1979 Cessna 182Q. I have owned it just over a year and logged about 90 hours. I love it. After about 50 hours I cracked a cylinder on takeoff. The O-470 engine had 1100 smoh. After weighing my options, I opted for a Factory Reman from Air Power. The engine is broken in with about 43 hours. CHTs and oil consumption has stabilized. Since the engine replacement i have noticed the oil temps are higher than the old engine. I only have the factory oil temp gauge but have CHT and EGT on all 6 cylinders. In cruise CHTs range from 330 to 370. However, the oil temp creeps up to a few needles off the 240 red line. It's in the green but toward the upper end. When I fly I am constantly watching it and obsessing. I just change the oil to Shell 100 plus from the mineral oil. I don't have much experience with the O-470 and just want someone to make me feel better. My mechanic does not seem to be concerned but says we will monitor it. I have attached a pic of the gauge after 40 minute cruise 65% power, 150 rich of peak and cowl flaps cracked open. OAT at 5500 feet was a warm 70 degrees. Any comments are appreciated.

Steve
 

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Calibrate your oil temp bulb with a candy thermometer, in a can of oil and a hot air gun.

see what it really is. prior to deciding on what to do.
 
Tom, does the typical Cessna sending unit and gauge of that era provide accurate calibration and predictable linearity? Although there's parallax in play, I would interpret the reading in the photo as 200° F, which seems normal.
 
I'm a dummy? You said you bought a factory reman and replaced your prior engine. Now you are comparing "normal" operating oil temperature of the two engines?

IMHO, if it's in the green, it's in the green, and the former occupant of your cowling is not a relevant data point.

@Ted DuPuis knows some engine stuffs. As does @Tom-D. How far off base am I?
 
Ideal oil temp is in the range of 180-190F - limits are not goals. That looks like about 220-230F, assuming the gauge is accurate. I agree with Tom that you should check the gauge to make sure that it's indicating accurately.

Assuming the gauge is accurate, first thing that comes to my mind is checking the baffling around the oil cooler. I find that most mechanics are extremely bad about paying attention to baffling. If you have air gaps around the oil cooler, basically at all, it's going to impact your cooling significantly.

The idea of "if it's in the green it's fine" is not ideal. You shouldn't get worked up about temps getting in the direction of redline, but if you're consistently seeing temperatures above ideal (for cylinders <380F is ideal, oil temp 180-190F like I said) then it's worth investigation. It's also worth investigation if oil temp is consistently below ideal, as too cold and it'll not boil the water out in-flight and that can lead to corrosion. Personally I'd rather have oil temp too high than too cold on these engines as I've seen far more damage done by corrosion than I have by hot oil/coking, especially on a 470 being a low power engine.
 
Ted DuPuis said:
Ideal oil temp is in the range of 180-190F - limits are not goals. That looks like about 220-230F, assuming the gauge is accurate. I agree with Tom that you should check the gauge to make sure that it's indicating accurately.

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Ted: Is this upstream or downstream of the oil cooler?

I am consistently seeing 195-205 upstream of the oil cooler on both engines on the Aztec (engine monitor) and 180 +/- on the factory gauges, which are after the oil cooler.

I've been told there is danger of the oil breaking down at temperatures in the 230 range?
 
GRG55 said:
Ted: Is this upstream or downstream of the oil cooler?

I am consistently seeing 195-205 upstream of the oil cooler on both engines on the Aztec (engine monitor) and 180 +/- on the factory gauges, which are after the oil cooler.

I've been told there is danger of the oil breaking down at temperatures in the 230 range?
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That's a good question. I believe that references the stock locations which are after the oil cooler. I can't remember where we put it in the lab but I think it was probably after, like where your factory gauge is.

Your numbers sound great. I wouldn't touch a thing.

Yes, past 230 there is worry about the oil breaking down. From a practical perspective on these things, on a low power naturally aspirated engine I don't worry about it too much. I ran my Aztec for a couple hundred hours with truly awful baffling - might as well have had none at all. The oil temp gauges were always pegged and my A&P just said "You can't trust those gauges they were never right." Same thing for CHT gauges, although those were only reading in the low 400s. Well, then I went through and redid the baffling, and I didn't even do half as good of a job as I later did on the 310 when I learned more about how to do baffling well. The plane gained 5 MPH IAS immediately, and the oil temp indication dropped 50 degrees. When I got my engine monitor I saw just how hot the CHTs were running...

Anyway, I put another 800 or so hours on the plane after that. The one engine did need a top overhaul shortly after, but those were really cheap cylinders the previous owner had put on despite only having 650 hours on them. The other engine I ran all the way past TBO without needing to touch the cylinders ever.
 
Ted DuPuis said:
That's a good question. I believe that references the stock locations which are after the oil cooler. I can't remember where we put it in the lab but I think it was probably after, like where your factory gauge is.

Your numbers sound great. I wouldn't touch a thing.

Yes, past 230 there is worry about the oil breaking down. From a practical perspective on these things, on a low power naturally aspirated engine I don't worry about it too much. I ran my Aztec for a couple hundred hours with truly awful baffling - might as well have had none at all. The oil temp gauges were always pegged and my A&P just said "You can't trust those gauges they were never right." Same thing for CHT gauges, although those were only reading in the low 400s. Well, then I went through and redid the baffling, and I didn't even do half as good of a job as I later did on the 310 when I learned more about how to do baffling well. The plane gained 5 MPH IAS immediately, and the oil temp indication dropped 50 degrees. When I got my engine monitor I saw just how hot the CHTs were running...

Anyway, I put another 800 or so hours on the plane after that. The one engine did need a top overhaul shortly after, but those were really cheap cylinders the previous owner had put on despite only having 650 hours on them. The other engine I ran all the way past TBO without needing to touch the cylinders ever.
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I am just working on the baffling on mine right now. Oil temps okay, but my main motivation is CHTs. They are always in the 400 range on most cylinders, and a bit higher on avg on the LH engine. The baffles are "okay", but now very stiff and lots of small leaks across the back especially. I am reworking them and trying to seal everything more carefully. But so far I am not seeing any dramatic change (I've got a whole spreadsheet of data from test flying at different altitudes and ambient temps as my baseline).

The one thing I am convinced of is that the cowls on my 1979 are not a very good design. With the cowl flaps closed there's hardly any outlet area, and the CHTs skyrocket, even at economy cruise at modest altitudes at the moderate temps up where I live. Other than in the dead of winter I have to fly it with the cowl flaps at 1/2 or fully open all the time.

The other variable I am not sure about is the engine monitor temp sensors. This JPI 760 unit was installed prior to my owning the plane. It uses sparkplug gasket thermocouples, and they are on the lower sparkplugs.

Any observations or thoughts on all this appreciated!
 
@GRG55 the Aztec cowling is a terrible design. Another falsehood my A&P said was that baffles didn't matter on these old planes they had so much air that baffles didn't matter. Nothing could be further from the truth. Sure the air inlets were mostly big, but they were poorly designed.

Once I got the baffling worked out on my Aztec I was able to maintain 380F or less on the hottest head with LOP ops. Sometimes I'd have to run the cowl flaps half open (especially in the summer or when >10k MSL) so don't be afraid to use that as an option. That said, while I advocate <380F for both Lycoming and Continentals, reality is for Lycoming <400F is fine, and it's what the manual recommends.

Get yourself some RTV and plug up any hole you can. If you're seeing scalloping between the flexible baffles and the top of the cowl, just replace that whole silicone part so that it's flush.

On the 310 I used the McFarlane CowlSaver flexible baffling. I saw it at Oshkosh and the way it was designed made sense for trying to make a more rigid seal while not rubbing holes in the cowl.

https://www.mcfarlaneaviation.com/products/product/CS085X3GBF/
 
3393RP said:
Tom, does the typical Cessna sending unit and gauge of that era provide accurate calibration and predictable linearity?
Click to expand...
There are two styles, the old bulb type are pretty good, the new electrical one not so much.
 
Bought my plane in September last year so this was my first time flying her in the summer. In the winter my oil temps were always 175-185 and oil pressure 75PSI. First real hot day I flew the plane and 20 hours after a cylinder replacement I was seeing 67psi and 215 temps so I pulled the POH to make sure it was all in specs and it was. Was alarming at first to see such a lower oil pressure.
 
What a great website. I have never posted before. Thank you for all the advice. I think the baffling is the right place to start but I believe the oil cooler sits right behind the prop in the open cowl. I was hoping the mineral oil was the problem but no luck. It is due for annual next month and I am going to get to the bottom of it. Thanks again!
 
Piper uses felt on many models as the perimeter baffle-cowl seal. If you take a piece and try to blow through it, there's almost no resistance. It would seem to me that such a baffle system would be incredibly leaky, raising cyl head temps while maybe reducing the rear engine accessory temps. Anybody else thought about this? I like Cessna's scheme of at least making the baffling as tight as practical
 
Steven R said:
Hello all. I have a 1979 Cessna 182Q. I have owned it just over a year and logged about 90 hours. I love it. After about 50 hours I cracked a cylinder on takeoff. The O-470 engine had 1100 smoh. After weighing my options, I opted for a Factory Reman from Air Power. The engine is broken in with about 43 hours. CHTs and oil consumption has stabilized. Since the engine replacement i have noticed the oil temps are higher than the old engine. I only have the factory oil temp gauge but have CHT and EGT on all 6 cylinders. In cruise CHTs range from 330 to 370. However, the oil temp creeps up to a few needles off the 240 red line. It's in the green but toward the upper end. When I fly I am constantly watching it and obsessing. I just change the oil to Shell 100 plus from the mineral oil. I don't have much experience with the O-470 and just want someone to make me feel better. My mechanic does not seem to be concerned but says we will monitor it. I have attached a pic of the gauge after 40 minute cruise 65% power, 150 rich of peak and cowl flaps cracked open. OAT at 5500 feet was a warm 70 degrees. Any comments are appreciated.

Steve
Click to expand...
I just went through this with a Cherokee 6 (Lyc O540). I started by replacing the Vernatherm valve with no improvement. In retrospect, you can remove this valve and check if you have a uniform, unpitted ring created by the valve seating ... if so, you are probably ok. However, you still run the risk that the valve is not closing at the correct temperature. I then replaced the oil cooler. Supposedly, the oil cooler should be replaced every 4 years. This yielded a slight improvement. Finally, I removed and cleaned the oil pressure regulator. I increased the oil pressure which was running on the low side (60 PSI) when heated up to around 180 plus degrees. Increasing the oil pressure increases oil flow through the engine/oil cooler. This did the trick. Oil temps dropped by 19 degrees. This is an easy adjustment to make. I also recommend Aeroshell 15W50 oil since it is multi-viscosity.

I am assuming that you baffling has been fully checked out. Also, check out the accuracy of your oil temp gauge. Mine was VERY accurate. The best way to check it is to remove the sensor and run extension leads outside the plane. This approach tests both the sensor and the gauge. Place the sensor in a pot of hot water. I used a (cheap) digital meat thermometer accurate to within +/- 2 degrees. I photographed the gauge reading inside the plane (eliminates parallax) and used a digital micrometer to linearly interpolate the photographed gauge scale for accuracy (my gauge has 75, 180, 260 degrees ... big gaps).

This problem drove me nuts for weeks. Hope this helps.
 
Welcome to the board John.

I think this thread is about 15 months old, but good information. The date is in the bottom left of the post.

Where are you from?
 
UPDATE

Thank everyone for the great advice. I have figured out the problem and thought I would post an update.

My mechanic checked the baffling and sealed one small leak. It had no effect. Next, he heated the oil temp probe to 200 degrees and marked the gauge in the cockpit for me. I felt a little better because the cruise temp was about 210 degrees on a hot day. A little warm for my liking but tolerable. I assumed it would run cooler as winter approached.

Please don't yell at me for this next part. This plane is my first constant speed prop and I don't have that much time in it. I was flying with a friend of mine who has thousands of hours in a 182. At cruise he said we were having to put in way too much throttle to get 21 inches at our 4500 altitude. He told me to have the gauge checked. I did. It has been reading a full 2 inches low for who knows how long. I have been running 21 inches and 2250 rpm, when in reality it was more like 23 inches (top of green), or more. That is a lot of cruise power on a hot California day. I had the manifold pressure gauge rebuilt and now, with proper cruise settings, the oil temp had returned to normal.

The reality is I was running 75 or even 80 percent power on a hot day. The oil temp was higher than normal. Kinda what you would expect running it so hard. I had the engine bore scoped and compression tested. Everything is fine. The only draw back is my plane is not as fast as I thought it was.

Thanks again. I am just glad the problem is solved for a $600 manifold pressure gauge rebuild.
 
If you plot one temperature on an original Cessna gauge? You have no idea what any other needle position means. And here’s a curve for you. If you don’t like where your gauge needle sits? Change the sender. Every sender is different. That isn’t confidence inspiring. If you want accuracy of information, get digital temp and pressure instruments.
 
High oil temp readings with electric gauges are often due to poor engine-airframe grounding. The normal electron flow is from airframe ground into the engine case, into the sender's threaded end, out of the sender's terminal, through the wire to the gauge's sender terminal, out of the gauge's + terminal to the bus and then to the battery +. The alternator is also grounded to the engine and pumps electrons backwards through the engine's case into the airframe, to the battery -, through the battery backwards (to charge it) and thence to the ammeter and bus and from there to the alternator +.

Trace it out, add a hair of resistance to the engine/airframe grounding, and you see that an alternate path is through that temp sender and gauge. It only takes a tiny bit of extra current through that circuit to drive the gauge up to a false reading.

Cessna had a service letter describing the installation of a dedicated ground wire between the engine case near the sender to the gauge case. Just a small wire to eliminate the ground potential differential. A good cleaning of the engine grounding would also be recommended, and that would also enhance starter performance.
 
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